The continuing trend of scaling down integrated circuits has forced the semiconductor industry to consider new techniques for fabricating precise components at submicron levels. Along with the need for smaller components, there has been a growing demand for devices requiring less power consumption. In the manufacture of transistors, these trends have led the industry to refine approaches to achieve thinner cell dielectric and gate oxide layers.
In dynamic semiconductor memory storage devices it is essential that storage node capacitor cell plates be large enough to retain an adequate charge (or capacitance) in spite of parasitic capacitances and noise that may be present during circuit operation. As is the case for most semiconductor integrated circuitry, circuit density is continuing to increase at a fairly constant rate. The issue of maintaining storage node capacitance is particularly important as the density of DRAM arrays continues to increase for future generations of memory devices.
The ability to densely pack storage cells while maintaining required capacitance levels is a crucial requirement of semiconductor manufacturing technologies if future generations of expanded memory array devices are to be successfully manufactured.
One method of maintaining, as well as increasing, storage node size in densely packed memory devices is through the use of "stacked storage cell" design. With this technology, two or more layers of a conductive material such as polycrystalline silicon (polysilicon or poly) are deposited over an access device on a silicon wafer, with dielectric layers sandwiched between each poly layer.
Though stacked (capacitor) storage cells are promising candidates to achieve sufficient storage capacitance in a limited area, as the DRAM cell size shrinks, scaling of the stacked capacitor structures is becoming more difficult.
Conventionally, it is known that the storage capacitance can be enhanced by using Hemi-Spherical Grain (HSG) silicon to form the storage node electrode without increasing the area required for the cell or the storage electrode height. The available methods include use of Low Pressure Chemical Vapor Deposition (LPCVD), engraving storage electrodes using poly film followed by P-diffusion utilizing POCl.sub.3 source gas, a mixture of spin-on-glass (SOG), coating the polysilicon with resist, and HSG formation by sequent high vacuum annealing. These methods however, are plagued due to formation of HSG silicon only on the inside of the storage node structure and thinning of the electrode itself.